What we know about the coronavirus
called 2019 nCoV changes hour by hour,
making it hard to predict how far the virus might spread
and how many people could become infected.
One Chinese government expert, Zhong Nanshan,
says the epidemic may peak towards the second week
of February, but academics from the University of Hong Kong,
think that's more likely to happen sometime
in April or May.
There is so much uncertainty about this new virus,
that it's almost impossible to make accurate predictions.
First of all, we don't know how many people
have the virus right now.
Reported cases have surged in the last few days,
but that could be down to increased surveillance
and testing.
There could still be thousands who aren't coming forward,
either because they have mild symptoms
or because they feel safer waiting it out at home.
Next, we don't know how easily the virus spreads.
On average, it looks as though each infected person
has the ability to infect two or three more.
This is known as the reproduction number,
and it's significant.
Up until now the number of infections
is thought to have doubled every six days.
That gives us some really big numbers.
Mass quarantines, the extended public holiday,
plus putting the public on high alert
may slow the spread of disease from person to person,
but it's hard to know how effective these measures will
be because of another big unknown.
We don't yet know how long it takes for an infected person
to show symptoms, nor whether that person can
pass the disease on before showing any signs of illness.
This raises doubts over the value
of temperature screening, which has been a key control so far.
Finally, we don't know how severe the virus is.
It seems to be spreading faster and wider
than Sars, which infected 8,000 people over eight months.
This coronavirus has gone past that number
in less than two months.
Around 20 per cent of patients progressed
from fever and a dry cough to more severe symptoms
such as pneumonia and organ failure with around 4
per cent dying, but at the start of an outbreak
serious cases tend to appear first,
like the tip of an iceberg.
So the rate of severe illness may
drop as milder cases turn up.
In Sars, the death rate was about 10 per cent,
but even if this new virus has a lower mortality rate,
it could still kill more people because it
causes more infections.
And while it's spreading, it might also
mutate to become more or less virulent.
We are better prepared than we were in 2003 during the Sars
epidemic, but this still looks like a monumental global health
challenge.
And until we know more about the virus itself,
its final impact will be hard to predict.